A 75-year-old man with interstitial pneumonia and enlarged mediastinal lymph nodes underwent endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA). He developed a high-grade fever seven days after EBUS-TBNA was performed; laboratory and radiologic findings showed intense inflammatory reactions, with swelling of the mediastinal lymph nodes on chest computed tomography. Mediastinal lymph node abscess was diagnosed, and it worsened in spite of systemic antibacterial treatment. Surgical treatment using a median sternotomy was performed, and the cultivation of surgically obtained mediastinal lymph node abscess fluid revealed Streptococcus intermedius. Combined treatment with antibiotics and surgical treatment was effective, leading to remission.